Method, apparatus and system for uplink rank adaptation

ABSTRACT

A method, an apparatus and a system for uplink rank adaptation are provided in the present invention, wherein the method comprises: estimating the maximum supportable data rate and channel information of a user equipment in uplink transmission; comparing the maximum supportable data rate with one or more predetermined thresholds, wherein the predetermined thresholds are associated with corresponding ranks; and determining a rank used by the user equipment in the uplink transmission based on a result of the comparison and the estimated channel information. With the present invention, a base station can quickly determine a rank for uplink MIMO transmission, decrease the rank estimating error, and lower the computation complexity for estimating the rank and the subsequent pre-coding vector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 14/232,767filed Jan. 14, 2014, which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to wireless communication field.More particularly, the present invention relates to a method, anapparatus and a system for uplink rank adaptation of user equipment.

BACKGROUND OF THE INVENTION

With the evolution of the High Speed Packet Access (HSPA), in the RAN#50meeting of the 3rd Generation Partnership Project (3GPP), the close looptransmits diversity (CLTD) was proposed as a work item and the uplinkMultiple-Input Multiple-Output (MIMO) was proposed as a study item. Forthe uplink MIMO, since a plurality of data streams (e.g. two datastreams) can be transmitted simultaneously from a user equipment to abase station under good channel quality, the user equipment can obtain anotable gain from the high bit-rate transmission of the uplink. How toflexibly select or determine the number of appropriate data streams(hereinafter referred to as “streams”), e.g. how to determine whethersingle-stream transmission or multiple-stream transmission is to beconducted in uplink transmission, it involves an uplink rank adaptationtechnology.

Rank generally represents the number of independent channels forwireless communication between the user equipment and the base stationin a multiple-antenna system, while rank adaptation relates to flexiblyselect from a plurality of ranks a rank for wireless communicationbetween the user equipment and the base station. Taking rank 1 and rank2 transmission of the uplink as an example, the rank 1 represents thatthe user equipment transmits data to the base station using a singlestream, now the same data is transmitted via different antennas andthereby achieves space diversity, while the rank 2 represents that theuser equipment transmits two different streams to the base station andthereby achieves space multiplexing. In addition, the rank with othernumerical values may also exist, e.g. rank 4.

In the downlink MIMO of the HSPA, the rank adaptation technologyinvolves that a base station (e.g. a serving Node-B) selects anappropriate rank for downlink MIMO transmission based on the feedbackinformation received from the user equipment, e.g. the user equipment'spreferred rank and a Channel Quality Indicator (CQI) as well as acorresponding Pre-Coding Indicator (PCI) for single-stream ormultiple-stream transmission. Since enough information including theabove information can be obtained at the base station, it would be easyfor the base station to determine the rank for the downlinktransmission.

Compared to the above case of downlink MIMO rank adaptation, in the caseof uplink MIMO rank adaptation, the base station is capable ofunderstanding better about the channel condition, but regarding the basestation determining an appropriate rank and a corresponding pre-codingvector, the related information obtained from the user equipment isrelatively inadequate and the frequency for obtaining the relatedinformation is relatively low. Such related information, for example,may include Uplink Power Headroom (UPH), use equipment buffer status anda transmission grant. For UPH, in the current standard specification, itis reported at a long period (e.g. once 100 ms) or based on eventtriggering so that the base station will not frequently receiveinformation about UPH. For the use equipment buffer status and thetransmission grant, the current user equipment does not report them tothe base station. Thus, the base station cannot rapidly obtainsufficient information from the user equipment so as to accuratelydetermine an appropriate rank, and the base station may select anincorrect rank to perform uplink MIMO transmission. Thereby, the uplinkMIMO performance is deteriorated and the gain obtained by MIMO isdecreased.

In addition, generally speaking, the user equipment should follow therank determined by the base station for uplink transmission. However,due to the possibility of lacking related information of the userequipment, the rank determined by the base station cannot always bewell-suited for the user equipment. Thus, in some cases, the wirelessnetwork should allow the user equipment to flexibly change the rank foruplink transmission based on the rank selected by the base station.

SUMMARY OF THE INVENTION

It is an object of the embodiments of the present invention to provide amethod, apparatus and system for uplink rank adaptation, which enables abase station to quickly and accurately determine a rank for uplink MIMOtransmission so that a user equipment can perform the uplink MIMOtransmission on the correct rank and obtain the gain of the uplink MIMOhigh speed data transmission.

To achieve the above object, according to one aspect of the embodimentsof the present invention, there is provided a method for uplink rankadaptation, comprising:

estimating a maximum supportable data rate and channel information of auser equipment in uplink transmission;

comparing the maximum supportable data rate with one or morepredetermined thresholds, wherein the predetermined thresholds areassociated with corresponding ranks; and

determining a rank used by the user equipment in the uplink transmissionbased on a result of the comparison and the estimated channelinformation.

According to another aspect of the embodiments of the present invention,there is provided an apparatus for uplink rank adaptation, comprising:

an estimator configured to estimate the maximum supportable data rateand channel information of a user equipment in uplink transmission;

a comparator configured to compare the maximum supportable data ratewith one or more predetermined thresholds, wherein the predeterminedthresholds are associated with corresponding ranks; and

a determiner configured to determine a rank used by the user equipmentin the uplink transmission based on a result of the comparison and theestimated channel information.

According to a further aspect of the embodiments of the presentinvention, there is provided a base station comprising the apparatus foruplink rank adaptation as described above.

According to one aspect of the embodiments of the present invention,there is provided a system for uplink rank adaptation, comprising:

a base station;

a user equipment for wireless communication with the base station;

wherein the base station comprises:

an estimator configured to estimate the maximum supportable data rateand channel information of a user equipment in uplink transmission;

a comparator configured to compare the maximum supportable data ratewith one or more predetermined thresholds, wherein the predeterminedthresholds are associated with corresponding ranks; and

a determiner configured to determine a rank used by the user equipmentin the uplink transmission based on a result of the comparison and theestimated channel information;

the user equipment performing the uplink transmission based on the rankdetermined by the base station.

According to a further aspect of the embodiments of the presentinvention, there is provided a method for uplink rank adaptation,comprising:

receiving an indication from a base station, wherein the indicationenables a user equipment to change a rank determined by the base stationfor uplink transmission; and

changing the rank for the uplink transmission based on one or morepredetermined thresholds.

According to the method, apparatus and system in embodiments of thepresent invention, the base station can quickly determine a rank foruplink multiple-antenna transmission by estimating the maximumsupportable data rate of the user equipment in combination with the rankthat a wireless channel can support. Since the process of estimating therank is relatively simple, embodiments of the present invention decreasethe computation complexity for estimating the rank, and since afterdetermining the rank, an appropriate pre-coding vector can be computedand determined merely for the determined rank, and thus the computationcomplexity for determining the pre-coding vector is also decreased. Inaddition, in the preferred embodiments of the present invention, thecommunication information or status of the user equipment side isconsidered as sufficiently as possible in the process of estimating themaximum supportable data rate of the user equipment, and thus the rankestimating error is also decreased.

When the base station authorizes the user equipment to change the rankspecified by the base station, embodiments of the present invention addthe flexibility for selecting the uplink rank, and further improve theaccuracy for selecting the rank and the link transmission gain broughtwhereby.

Other features and advantages of the present invention will becomeapparent by making references to the detailed description of embodimentsof the present invention in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an exemplary multiple-antennasystem (e.g. MIMO system) for uplink rank adaptation that may be appliedto embodiments of the present invention;

FIG. 2 is a flowchart illustrating a method for uplink rank adaptationaccording to embodiments of the present invention;

FIG. 3 is a flowchart illustrating a method for estimating a maximumsupportable data rate according to an embodiment of the presentinvention;

FIG. 4 is a flowchart illustrating a method for estimating a maximum

FIG. 5 is a block diagram illustrating an apparatus for uplink rankadaptation according to embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Specific embodiments of the present invention will be described below indetail by making references to the accompanying drawings.

FIG. 1 is a block diagram illustrating an exemplary multiple-antennasystem 100 (e.g. MIMO system) for uplink rank adaptation that may beapplied to embodiments of the present invention. The multiple-antennasystem 100, for example, may be applied to wireless access systems suchas High Speed Packet Access (HSPA), code division multiple access (CDMA)2000 and long-term evolution (LTE), etc. As illustrated in FIG. 1, themultiple-antenna system 100 comprises Node B 101 (i.e. base station) andUser Equipment (UE) 102 in wireless communication with the Node B,wherein the Node B 101 has N antennas while UE 102 has M antennas tothereby constitute a N×M Multiple-Input Multiple-Output (MIMO) system.In a HSPA system, it, for example, may constitute a 2×2 MIMO system,where N and M equal to 2 indicates that the MIMO system supportssingle-stream or dual-stream transmission, i.e. the value of a rank maytake 1 or 2 as appropriate.

In the illustrated multiple-antenna system 100, the Node B 101 mayestimate the maximum supportable data rate and channel information ofthe UE 102 in uplink transmission by related information received fromthe UE 102, compare the maximum supportable data rate with one or morepredetermined thresholds (associated with corresponding ranks), anddetermine the rank of the UE 102 in the uplink transmission based on thecomparison result and the channel information. The above operations ofthe Node B 101 may be performed respectively by an estimator 501, acomparator 502 and a determiner 503 of the apparatus 500 as illustratedin FIG. 5, which will be described below in detail with reference toFIG. 5.

In one embodiment of the present invention, the related informationreceived from the UE 102 may involve information such as the uplinkpower headroom, the transmit buffer status and the uplink transmissiongrant of the UE 102, while the channel information may be expressed by achannel matrix, which may be estimated by a base station based on thepilots and the pre-coding matrix. In another embodiment of the presentinvention, when the UE 102 is instructed or authorized to change therank determined or indicated by the Node B 101, the UE 102 may, forexample, change the size of the rank for the uplink transmission when apredetermined condition is met. It will be described below in detail bymaking references to FIGS. 2 and 4 that how the Node B 101 rapidlydetermines a rank adapted to be used by the UE 102 in the uplinktransmission in the exemplary multiple-antenna system 100.

FIG. 2 is a flowchart illustrating a method 200 for uplink rankadaptation according to embodiments of the present invention. Asillustrated in FIG. 2, the method 200 starts at step S201, and at stepS202, the method 200 estimates the maximum supportable data rate andchannel information of a user equipment (e.g. UE 102) in uplinktransmission, wherein one example for estimating the maximum supportabledata rate may involve estimating the maximum supportable data rate basedon the estimation of the uplink power headroom, the transmit bufferstatus and the uplink transmission grant of the user equipment (how toestimate will be described below in detail by making references to FIGS.3 and 4), and the high maximum supportable data rate requires high UPH,more buffered data and high transmission grant.

The channel information, for example, may be the channel matrix Hobtained by utilizing the reference signal. Take a 2×2 multiple-antennasystem as an example, the channel matrix may be expressed as below:

$\begin{matrix}{H = \begin{bmatrix}h_{11} & h_{12} \\h_{21} & h_{22}\end{bmatrix}} & (1)\end{matrix}$

Here h denotes a wireless channel between the transmit antenna i (i=1,2) and the receive antenna j (j=1, 2). The number of supportableindependent channels of the current wireless channel, i.e. the number ofsupportable streams can be determined by calculating the size of therank of the channel matrix. Regarding the estimation and determinationof the channel matrix, those skilled in the art may employ appropriatemeans to implement them. Further explanations will not be made hereinfor avoiding unnecessarily obscuring the present invention.

Next, the method 200 proceeds to step S203. At step S203, the method 200compares the maximum supportable data rate with one or morepredetermined thresholds, wherein the predetermined thresholds areassociated with corresponding ranks. For example, a correspondingthreshold is respectively set for the rank 1, 2, 3 or 4, and when theestimated maximum supportable data rate exceeds certain correspondingthreshold, a rank corresponding to the threshold is selected.

At step S204, the method 200 determines a rank used by the userequipment in the uplink transmission based on a result of the comparisonand the estimated channel information. When the rank determined via apredetermined threshold is different from that determined via a channelmatrix, selecting a smaller rank of the two for the uplink MIMOtransmission. For example, when it is determined through the comparisonthat the maximum supportable data rate of the user equipment is higherthan the threshold predetermined for rank 1 but lower than the onedetermined for rank 2, and the rank of the estimated channel matrix is2, it can be determined that it is suitable for those skilled in the artto use rank 1 for transmission in the uplink MIMO transmission, that is,the user equipment would use single stream for transmission. Again, whenit is determined through the comparison that the maximum supportabledata rate of the user equipment is higher than the thresholdpredetermined for rank 2, and the rank of the estimated channel matrixis also 2, then it can be determined that it is suitable for the useequipment to use rank 2 for transmission in the uplink MIMOtransmission, that is, the user equipment will use dual streams fortransmission. Finally, the method 200 ends at step S205.

With the method 200 in the above embodiments of the present invention,the process of estimating the rank becomes relatively simple and therebydecreases the computation complexity for estimating the rank. Inaddition, since the rank for the uplink MIMO transmission is determined,the base station will unnecessarily try to select the preferredpre-coding vector from the codebook respectively for various possibleranks, but directly select a preferred pre-coding vector that maximizesa payload size from the codebook for the determined rank, thereby savingthe complexity and overhead in the calculation aspect for determiningthe pre-coding vector. For example, in the above case of determining orestimating the rank as 1, the base station will no longer try the uplinktransmission with the rank 2 or 3 respectively for each pre-codingvector in the codebook so as to determine an appropriate rank and acorresponding pre-coding vector after considering the rank 2 or 3.

Although it is not shown in FIG. 2, in one embodiment, the method 200further comprises that the base station dynamically indicates that theuser equipment has an authority for changing the rank, and theindication may be made via signaling, e.g. indicates that the userequipment has the authority for changing the rank via one of the RadioResource Control (RRC) signaling, a Media Access Control (MAC) layerheader, a High Speed Shared Control Channel (HS-SCCH). In anotherembodiment, the method 200 may inform the user equipment of one or morethresholds for determining whether to change the rank, via one of theradio resource control signaling, the media access control layer headerand the high speed shared control channel, wherein the one or morethresholds may, for example, include one or more thresholds about thebuffered data in the transmit buffer, the available uplink powerheadroom or the uplink transmission grant. With the above steps, theuser equipment has the authority for changing the rank for uplinktransmission and may change the rank based on one or more predeterminedthresholds, and thereby further improves the accuracy for selecting therank and the link transmission gain brought whereby.

Now, taking the rank 1 or 2 as an example to explain the case that theuser equipment has an authority for changing the rank. When the basestation indicates to the user equipment that the rank for the uplinktransmission is 1, it will not be allowed or indicated that the userequipment has an authority for changing the rank in any case. This isbecause when lacking the channel information and the correct pre-codingvector selection, the user equipment changing the rank from 1 (i.e.single-stream transmission) to 2 (dual-stream transmission) will causethe received data signal-to-noise ratio to obviously decrease due togreat interference between streams, since the rank of the uplink channelis not enough to support the transmission by the selected rank. Thus,the user equipment is only allowed to use the rank whose value is nothigher than the value indicated by the base station for transmission soas to ensure the rank of the channel not less than the rank selected bythe user as well as the uplink reliable transmission.

If the base station indicates to the user equipment that the rank forthe uplink transmission is 2, the user equipment may change the rank tobe 1 based on the configuration of the network. For example, on thebasis that the buffered data in the transmit buffer of the userequipment is less than the threshold predetermined for rank 2, or on thebasis that the available power headroom for dual-stream transmission(the rank is 2) is less than the threshold predetermined for rank 2, oron the basis that the transmission grant is less than the thresholdpredetermined for rank 2, the user equipment may change the rank from 2to 1, i.e. change from the dual-stream transmission to the single-streamtransmission.

In addition, the pre-coding vector to be used by the user equipmentafter the rank is changed may be predetermined. For example, the datastream (e.g. dual-stream) may sequentially use the pre-coding vector inthe pre-coding matrix indicated by the base station, that is, theprimary data stream can still use the primary pre-coding vector from thepre-coding matrix while the secondary data stream can use the secondarypre-coding vector from the pre-coding matrix.

FIG. 3 is a flowchart illustrating a method 300 for estimating themaximum supportable data rate according to one embodiment of the presentinvention. As illustrated in FIG. 3, the method 300 starts at step S301and estimates UPH of the user equipment at step S302.

In one embodiment, the estimation of UPH of the user equipment includesthe base station (or Node B) of serving user equipment estimating basedon Formula (2) below:

availableU PH=referenceU PH+StepSize×accumulate dTPC+A   (2)

Where availableUPH is the estimated UPH; referenceUPH is the referenceUPH, which is generated when the UPH is reported by the user equipmentto the Node B or is measured by the serving Node B; StepSize is an innerloop power control step; accumulatedTPC is an accumulation of transmitpower control commands; and A is the margin to compensate the estimationerror of UPH.

For accumulatedTPC in the above formula, controlling the increase of thetransmit power may be denoted by +1 while controlling the decrease ofthe transmit power may be denoted by −1, and the accumulating operationmay start from the time when the reference UPH is updated (i.e. reset);accumulatedTPC is reset to be zero each time when the reference UPH isupdated. In other words, accumulatedTPC is reset in response to updatingthe reference UPH.

For the reference UPH in the above formula, it should be updated asfrequently as possible in various cases in order to minimize theestimation error of UPH. For the updating of the reference UPH, it maybe updated via at least one of the following:

updating the reference UPH to be a new UPH of the report in response tothe user equipment reporting a new UPH to the Node B;

updating the reference UPH to be a measured UPH in response to measuringthe UPH of the user equipment. For example, when the user equipment ispower limited, the Node B can measure the UPH of the user equipmentbased on the received power of all physical channels, and then canupdate the reference UPH to be the measured UPH of the Node B.

The reference UPH may be updated based on Formula (3) below:

$\begin{matrix}{{TPO} = {\sum\limits_{c = 1}^{N}{{rxPower}_{{PCH},c}/{rxPower}_{R - {DPCCH}}}}} & (3)\end{matrix}$

Where TPO (Transmission Power Offset) is the transmission power offsetof the user equipment; N is the number of physical channels in uplink;rxPower_(PCH,c) is the received power of the Cth physical channel;rxPower_(R-DPCCH) is the received power of the reference DedicatedPhysical Control Channel (DPCCH) of the UPH, which can be the receivedpower of a single DPCCH or a certain combination of the received powersof certain DPCCHs. When the user equipment is detected to be powerlimited, the measured TPO equals the UPH. Even when the user equipmentis detected to be not power limited, the reference UPH still can beupdated conditionally by the above Formula (3). For example, if thetransmission power offset of the user equipment measured according toFormula (3) is larger than the present estimated UPH obtained accordingto Formula (2), the reference UPH can be updated to be the transmissionpower offset of the user equipment and accumulatedTPC can be reset as 0.

Subsequent to estimating the UPH of the user equipment, the method 300proceeds to step S303. At the step S303, the method 300 estimates thetransmit buffer status of the user equipment. Although the exact uplinkbuffer status of a user equipment is not reported to the Node Bcurrently, the transmit buffer status can be estimated by utilizingembodiments of the present invention according to at least one of thefollowing: a happy bit received from the user equipment; an EnhancedTransport Format Combination Indicator (E-TFCI) received from the userequipment; or the current service type of the user equipment.

Regarding the case of receiving the happy bit from the user equipment,when the user equipment transmits a negative happy bit to the Node B, itindicates that the number of the buffered bits in the transmit buffer ofthe user equipment has exceeded a predetermined threshold. That is tosay, the user equipment has buffered enough bits to support a highertransmit data rate in uplink. At that time, the predetermined thresholdreflects the transmit buffer status of the current user equipment.

Regarding the case of receiving E-TFCI from the user equipment, the NodeB can monitor the E-TFCIs transmitted from the user equipment. With thestatistic characteristics of the corresponding transport block sizes,the Node B can predict whether the user equipment has enough bufferedbits to support a high data rate transmission. For example, the Node Bcan measure the most recent uplink transmit data rate of the userequipment, and it is regarded that the buffered data of the userequipment at least can support the uplink data transmission at a ratenot less than the transmission rate. For another example, if the userequipment always transmits with the maximum allowed Enhanced TransportFormat Combination (E-TFC) which is identified by a high enough absolutetransmission grant, the base station can similarly regard that thebuffered data in the transmit buffer of the user equipment at least cansupport the uplink data transmission at a transmission rate not lessthan the absolute transmission grant. Thus, the Node B can estimate thetransmit buffer status of the user equipment by determining that thedata in the buffer supports the uplink transmission at a rate not lessthan the measured data rate.

Regarding the case of the current service type of the user equipment,since different service requires different Quality of Service (QoS), theservice type is also a beneficial factor to predict the transmit bufferstatus of the user equipment. For example, the bit-rate of a real timeservice varies quickly and there is a strict delay restriction, whichmeans that the predication of the buffer status may be based on the mostrecently instantaneous information. Take the real time videotransmission as an example, the uplink data transmission rate that canbe supported by the data in the transmit buffer of the user equipmentcan be estimated based on the most recent E-TFC sizes of certain TTIs,e.g. by sliding average or by utilizing the filter as illustrated inFormula (4) below:

Rate(n)=Rate(n−1)×(1−α)+α×TBsize/TTI_length   (4)

Where Rate is a supportable uplink data rate; n is a sequence number ofa current TTI; TBsize is a current transport block size; TTI_length is alength of a TTI; and a is a forgetting factor.

Next, the Node B estimates the transmit buffer status of the userequipment by determining that the data in the buffer supports the uplinktransmission at a rate not less than the measured data rate.

For a File Transfer Protocol (FTP) service as another example, the userequipment usually has enough buffered bits to support high data ratetransmission in uplink transmission during the time being served, i.e.can execute multiple-stream transmission. The uplink data transmissionrate that can be supported by the data in the uplink transmit buffer ofthe FTP service can also be estimated via the above Formula (4).Similarly, the Node B correspondingly estimates the transmit bufferstatus of the user equipment by determining that the data in the buffersupports the uplink transmission at a rate not less than the estimateddata rate.

Upon estimating the transmit buffer status of the user equipment, themethod 300 proceeds to step S304. At the step S304, the method 300estimates the uplink transmission grant.

The uplink transmission grant is another factor for limiting the maximumsupportable data rate of a user equipment. For the user equipment not insoft/softer handover, the Node B serving the user equipment can exactlyknow the transmission grant of the user equipment. However, for a userequipment in a soft handover, the transmission grant can also be changedby a non-serving Node B. In this case, the serving Node B may not knowthe transmission grant of the user equipment. According to embodimentsof the present invention, especially when the user equipment is in asoft/softer handover, the serving Node B can estimate the transmissiongrant of the user equipment based on one of the following:

when a user equipment is not power limited and it sends a negative happybit to the serving Node B, then the most recent maximum transport blocksize identifies the uplink transmission grant, and thereby the uplinktransmission grant of the user equipment can be estimated; or themaximum transport block size of the user equipment when it is powerlimited. For example, when the user equipment is power limited, thecorresponding transport block size of the uplink transmission grant canbe identified as larger than the maximum transport block size.

In the case that each stream in the singe-stream transmission (rankequal to 1) and multiple-stream transmission (rank greater than or equalto 2) provides a special or separate transmission grant, the estimationof the uplink transmission grant may additionally include respectivelyestimating the uplink transmission grant for the singe-streamtransmission or multiple-stream transmission.

Since the transmission grant does not change so often as the UPH and theuplink transmit buffer status, the measurement frequency of the uplinktransmission grant of the user equipment in a soft handover does notneed to be as high as the UPH and the uplink transmit buffer status.

After the method 300 estimates the UPH, transmit buffer status anduplink transmission grant of the user equipment respectively at stepsS302, S303, and S304, the method 300 respectively estimates the uplinkmaximum supportable data rate of the user equipment for the case of rankequal to 1 (i.e. single-stream transmission) and rank equal to N (i.e.N-stream transmission) at steps S305 and S306.

For the single-stream transmission of rank equal to 1, estimating themaximum supportable data rate in a Transmission Time Interval (TTI)includes an estimation according to Formula (5) below:

max DataRate_(ss) =f(availableUPH, NrofBufferedBits, SG_(ss))ITTI_length  (5)

Where max DataRate_(ss) is a maximum supportable data rate insingle-stream transmission; available UPH is estimated UPH;NrofBufferedBits is a estimated number of the buffered bits in thetransmit buffer (which, for example, is expressed by a supportable datarate); SG_(ss) is an uplink transmission grant estimated forsingle-stream transmission; TTI _length is a length of a TTI; f( ) isthe function that respectively maps available UPH, NrofBufferedBits andSG_(ss) to their respective maximum supportable data rates and takes theminimum value.

For the multiple-stream transmission of rank equal to N, estimating themaximum supportable data rate in a TTI includes an estimation accordingto Formula (6) below:

$\begin{matrix}{{\max \mspace{14mu} {DataRate}_{MS}} = {\sum\limits_{s = 1}^{N}{{f\left( {{UPH}_{s},{NrofBufferedBits}_{s},{SG}_{s}} \right)}/{TTI\_ length}}}} & (6)\end{matrix}$

Where max DataRate_(MS) is the maximum supportable data rate inmultiple-stream transmission; s is the serial number of the stream; N isthe number of the streams; UPH_(s) is the uplink power headroomestimated for the sth stream; NrofBufferedBits_(s) is the number of thebuffered bits in the transmit buffer estimated for the sth stream(which, for example, is expressed by a supportable data rate); SG_(s) isan uplink transmission grant estimated for the sth stream; TTI_length isa length of a TTI; f( ) is the function that respectively maps UPH_(s),NrofBufferedBits_(s) and SG_(s) to their respective maximum supportabledata rates and takes the minimum value.

Take N=2 as an example, i.e. in case of dual-stream transmission, theUPH and the buffered data are shared between two streams. Thetransmission grant may be shared between two streams if there is noseparate transmission grant defined respectively for the two streams.Then in the above formula, UPH_(s)=UPH₁+UPH₂=available UPH whileNrofBufferedBits=NrofBufferedBits₁+NrofBufferedBits₂, where thesubscripts 1 and 2 respectively denote stream 1 and stream 2.

After respectively estimating the uplink maximum supportable data ratesof the user equipment for rank equal to 1 and rank equal to N at steps305 and step S306, the method 300 ends at step S307.

With the method steps as illustrated in FIG. 3, the maximum supportabledata rates of the user equipment for rank equal to 1 and rank equal to N(N greater than and equal to 2) can be estimated, and thereby theoperation of estimating the maximum supportable data rate at step S202of the method 200 is achieved. Although steps S302-S304 are shown inorder in FIG. 3, it does not mean that the above steps can beimplemented only in the order as shown in FIG. 3, and they can also beimplemented in parallel or in other orders. In addition, although it isnot shown in FIG. 3, the method 300 can further estimate the maximumsupportable data rate of the user equipment with reference to thelimitation from the communication upper layer, and the limitation, forexample, may be the IuB bandwidth limit in case of high data ratetransmission. For example, if the bandwidth that the communication upperlayer can provide (i.e. the maximum supportable data rate) is less thanthe single-stream or multiple-stream maximum supportable data rate, themaximum supportable data rate of the uplink single-stream ormultiple-stream transmission equals to the bandwidth that thecommunication upper layer can provide.

FIG. 4 is a flowchart illustrating a method 400 for estimating themaximum supportable data rate according to another embodiment of thepresent invention. The method 400 starts at step S401, and at step S402,a maximum Signal to Interference plus Noise Ratio (SINR) is estimatedbased on the estimated channel information (i.e. channel matrix) anduplink power headroom, i.e. the maximum available equivalent Signal toInterference plus Noise Ratio is estimated. Next, at step S403, themethod 400 estimates a supportable data rate by utilizing the maximumSignal to Interference plus Noise Ratio.

At step S404, the method 400 estimates the maximum supportable data ratebased on the supportable data rate, transmit buffer status and uplinktransmission grant. Specifically speaking, the data rates correspondingto the obtained supportable data rate, transmit buffer status and uplinktransmission grant are compared, and when respective values aredifferent, selecting the minimum value as the maximum supportable datarate estimated in this embodiment of the present invention. Finally, themethod 400 ends at step S405. With the above steps of the method 400,the operation of estimating the maximum supportable data rate at stepS202 in the method 200 can be achieved.

In the above method 400, the channel information, the uplink powerheadroom, the transmit buffer status and the uplink transmission grant,for example, may be implemented by employing various methods asdescribed with reference to FIG. 3, while estimating the maximum Signalto Interference plus Noise Ratio, for example, may be calculated withFormula (7) below:

$\begin{matrix}{{SINR}_{s} = \frac{{{\begin{bmatrix}w_{1s} \\w_{2s}\end{bmatrix}^{H}\begin{bmatrix}{\sqrt{{Pu}_{s}}{\overset{\sim}{h}}_{1s}} \\{\sqrt{{Pu}_{s}}{\overset{\sim}{h}}_{2s}}\end{bmatrix}}\begin{bmatrix}{\sqrt{{Pu}_{s}}{\overset{\sim}{h}}_{1s}} \\{\sqrt{{Pu}_{s}}{\overset{\sim}{h}}_{2s}}\end{bmatrix}}^{H}\begin{bmatrix}w_{1s} \\w_{2s}\end{bmatrix}}{\begin{bmatrix}w_{1s} \\w_{2s}\end{bmatrix}^{H}{{Ru}_{s}\begin{bmatrix}w_{1s} \\w_{2s}\end{bmatrix}}}} & (7)\end{matrix}$

where s is a serial number of the stream; Pu_(s) is transmit power ofthe stream s (which can be obtained via the uplink power headroom); Ruis a noise and interference covariance matrix; {tilde over (h)} is anequivalent channel matrix; numbers 1 and 2 are the serial numbers of thereceive antennas; W is the weighted weight estimated by the receiver.

where the noise and interference covariance matrix Ru_(s) may becalculated with Formula (8) below:

$\begin{matrix}{{Ru}_{s} = {\frac{1}{SF}\left( {R - {\sum\limits_{s^{\prime} = 1}^{2}{{{Pu}_{s^{\prime}}\begin{bmatrix}{\overset{\sim}{h}}_{1s^{\prime}} \\{\overset{\sim}{h}}_{2s^{\prime}}\end{bmatrix}}\begin{bmatrix}{\overset{\sim}{h}}_{1s^{\prime}} \\{\overset{\sim}{h}}_{2s^{\prime}}\end{bmatrix}}^{H}} + {\sum\limits_{{s^{\prime} = 1},{s^{\prime} \neq s}}^{2}{{SF} \cdot {{{Pu}_{s^{\prime}}\begin{bmatrix}{\overset{\sim}{h}}_{1s^{\prime}} \\{\overset{\sim}{h}}_{2s^{\prime}}\end{bmatrix}}\begin{bmatrix}{\overset{\sim}{h}}_{1s^{\prime}} \\{\overset{\sim}{h}}_{2s^{\prime}}\end{bmatrix}}^{H}}}} \right)}} & (8)\end{matrix}$

where s and s are the serial numbers of the streams; SF is a spreadingfactor; R is an autocorrelative matrix of the receive signal.

Regarding using the maximum Signal to Interference plus Noise Ratio toestimate the supportable data rate, in one embodiment, the supportabledata rate can be estimated by the Signal to Interference plus NoiseRatio and the Shannon formula. In another embodiment, the supportabledata rate can be estimated by the Signal to Interference plus NoiseRatio and the E-TFC selection look-up table. For example, the Signal toInterference plus Noise Ratio required by each transport format in theE-TFC table can be estimated in advance according to the predeterminedBlock Error Rate (BLER) target, and then the current available maximumSignal to Interference plus Noise Ratio is estimated based on Formula(7). For each transmission rank that may be selected, the Signal toInterference plus Noise Ratio is allocated to each stream according tocertain rules (e.g. an equal division manner), and then the maximumtransport format of each stream can be obtained by looking up the table,and further the supportable rate can be obtained if using the rank fordata transmission.

FIG. 5 is a block diagram illustrating an apparatus 500 for uplink rankadaptation according to embodiments of the present invention. Asillustrated in FIG. 5, the apparatus 500 comprises an estimator 501, acomparator 502 and a determiner 503, wherein the estimator 501 isconfigured to estimate the maximum supportable data rate and the channelinformation of a user equipment in uplink transmission; the comparator502 is configured to compare the maximum supportable data rate with oneor more predetermined thresholds, wherein the predetermined thresholdsare associated with corresponding ranks; the determiner 503 isconfigured to determine a rank used by the user equipment in the uplinktransmission based on a result of the comparison and the estimatedchannel information. In one embodiment, the apparatus 500 may beimplemented as a base station or implemented in a base station, e.g. theNode B 101 of the multiple-antenna system as illustrated in FIG. 1.

In one embodiment of the present invention, the estimator 501 isconfigured to estimate the maximum supportable data rate based on theestimation of the uplink power headroom, transmit buffer status anduplink transmission grant of a user equipment.

In another embodiment of the present invention, the estimator 501 isconfigured to estimate the maximum supportable data rate with Formula(5) for single-stream transmission. In a further embodiment of thepresent invention, the estimator 501 is configured to estimate themaximum supportable data rate with Formula (6) for multiple-streamtransmission.

In one embodiment of the present invention, the estimator 501 isconfigured to estimate the maximum Signal to Interference plus NoiseRatio based on the estimated channel information and uplink powerheadroom, to estimate the supportable data rate utilizing the maximumSignal to Interference plus Noise Ratio, and to estimate the maximumsupportable data rate based on the supportable data rate, transmitbuffer status and uplink transmission grant. That is, the estimator 501can be used to implement respective steps of the method 400.

Embodiments of the present invention are described above with referenceto the accompanying drawings. It should be noted that to facilitate theunderstanding of the present invention, some more specific technicaldetails that are well-known to those skilled in the art and may benecessary for implementing the present invention are omitted in theabove descriptions.

The present invention may employ a form of complete hardwareembodiments, complete software embodiments, or both. In a preferredembodiment, the present invention is implemented as software, including,without limitation to, firmware, resident software, micro-code, etc.

The specification of the present invention is provided for explanationand description purposes, rather than exhausting or limiting the presentinvention as the disclosed form. For those of ordinary skill in the art,many modifications and changes are available.

Therefore, selecting and describing the embodiments is to better explainthe principle and the actual application of the present invention, andto enable those of ordinary skill in the art to understand that, withoutdeparture from the essence of the present invention, all modificationsand changes fall into the protection scope of the present inventiondefined by the claims.

What is claimed is:
 1. A method for uplink rank adaptation, comprising:receiving, by a user equipment (UE) from a base station, a rank foruplink transmission; changing, by the UE, the rank for uplinktransmission to be different from the rank received from the basestation based on one or more predetermined thresholds; and using, by theUE, the changed rank for wireless communication of the user equipment inthe uplink transmission.
 2. The method of claim 1, wherein the one ormore predetermined thresholds comprise one or more predeterminedthresholds about buffered data in a transmit buffer and available uplinkpower headroom of the UE.
 3. The method of claim 1, wherein changing therank for uplink transmission based on one or more predeterminedthresholds comprising: changing the rank for uplink transmission inresponse to determining that at least one of buffered data and availableuplink power headroom is less than the one or more predeterminedthresholds.
 4. The method of claim 3, wherein the determination of thebuffered data being less than the one or more predetermined thresholdsis based on an enhanced transport format combination indicator (E-TFCI)of the UE.
 5. The method of claim 1, wherein the user equipment is in amultiple-input multiple-output (MIMO) system.
 6. The method of claim 1,further comprising: receiving, by the UE, a preferred precoding vectorfor uplink transmission.
 7. The method of claim 1, wherein the rank foruplink transmission received from the UE is higher than the changedrank.
 8. The method of claim 1, wherein the rank received from the basestation is rank 2, which is changed to rank 1 by the UE.
 9. The methodof claim 1, further comprising: transmitting, by the UE, at least one ofan uplink power headroom and a transmit buffer status to the basestation prior to the receipt of the rank for uplink transmission. 10.The method of claim 1, further comprising: transmitting, by the UE, oneor more pilot signals to the base station prior to the receipt of therank for uplink transmission.